In the conventional color diffusion transfer process and heat development transfer process, diffusible dyes formed or released imagewise through development of a light-sensitive element after exposure are diffused and transferred into a dye fixing layer containing a mordant or a dye-accepting polymer. Dye images are observed after the dyes have been transferred and fixed in the dye fixing layer.
The appearance of the surface, be it glossy or mat one, is selected depending on the end-use purpose of the dye fixing element, the user's preference, and so on.
Though addition of a matting agent has so far been known as one of the matting methods, the most inexpensive and effective method is such that unevenness is given to the support surface through embossment processing performed in the course of the production of the support. Therein, however, a dye fixing layer with a smooth surface is not obtained, because when a dye fixing layer constituted by a mordant and a binder is provided on a support whose surface has been rendered uneven by the embossment processing, the dye fixing layer surface opposite to the interface between the support and the dye fixing layer also becomes uneven corresponding approximately to the unevenness of the support surface. The case wherein the dye fixing element poor in surface smoothness is superimposed on a light-sensitive element, and diffusible dyes produced in the light-sensitive element are transferred into the dye fixing element to form the dye images, causes a problem of generating transfer marks (or such uneven density as to have white spots in colored areas corresponding to concaved spots).
In the heat development transfer process in particular, a preferably used method involves containing in the image forming reaction system as a base precursor a combination of a basic metal compound slightly soluble in water and a compound capable of undergoing in water as a medium the complexing reaction with the metal ion constituting said slightly soluble metal compound (which is abbreviated as "complexing compound", hereinafter), and raising the pH of the reaction system by allowing these two compounds to react with each other upon heating. (In order to prevent these slightly soluble metal compound and complexing compound from reacting with each other prior to development-processing, it is desirable that the slightly soluble metal compound should be incorporated in, e.g., a light-sensitive element, and the complexing compound in, e.g., a dye fixing element having a support other than that of the light-sensitive element.) However, when the dye fixing element poor in surface smoothness is superimposed upon the light-sensitive element, an increase in pH through the reaction between the foregoing compounds occurs in the convex part, but little occurs in the concave part. Thereby, an ununiform distribution of an alkali concentration is caused at the interface between both elements to result in a serious problem of considerable generation of dye-image transfer marks.
On the other hand, the method of forming a mat surface by addition of matting agent particles causes transfer marks similar to those described above when the particle size of the matting agent is relatively large, compared with the thickness of the dye fixing layer, whereas when the particle size is relatively small the method cannot achieve a sufficient matting effect. Moreover, the method of using a matting agent in the outermost layer generally causes a sharp drop of the maximum image density.
Accordingly, even in these methods of adding a matting agent, dye fixing elements with a uniform mat surface, which exhibit high image density and no transfer mark, have not been obtained yet.